Power requirements and size are critical design parameters in portable electronic devices such as pagers and broadcast frequency modulation (FM) radio receivers. In an increasingly energy conscious world, these two design parameters are also important in other electronic devices that operate when plugged into an alternating current (AC) supply.
A circuit that is often used within integrated circuits in such devices is a one-half supply voltage reference, also described herein as a voltage splitter. Such a circuit is particularly useful when a signal is needed in an analog circuit that must represent both positive and negative polarities, when the analog circuit has only one power supply. When a reference voltage level of one-half of the power supply voltage is established, positive deviations from the reference level can be used to represent positive polarities and negative deviations can be used to represent negative polarities. Equivalent maximum deviations for both positive and negative polarity signals are conveniently allowed when the reference voltage level is established as near to one-half the power supply voltage as is practicable. The reference voltage must be capable of supplying some amount of current (which is usually relatively small), and must be relatively noise free. One technique for supplying such a reference voltage is to use a well known resistor divider with two equal resistors. The precision of the resistor divider is directly related to the precision of the resistors, and the output impedance of the resistor divider is directly related to the value of the resistances used. However, for a resistor divider having an output impedance of, for example, 2.5 MegOhms, the area of the 5 MegOhm divider resistors, even when they are implemented having the smallest practical surface area, is very large in comparison to transistors and capacitors in modern integrated circuits, and the tolerance of the ratio of the divider is on the order of a few percent.
Thus, what is needed is a voltage splitter circuit that is small and requires little power to operate.